In the pursuit of achieving zero emissions, exploring the concept of recycling metal waste from industries and workshops (i.e., waste-free) is essential. This is because metal recycling not only helps conserve natural resources but also requires less energy as compared to the production of new products from virgin raw materials. The use of metal scrap in rapid tooling (RT) for injection molding is an interesting and viable approach. Recycling methods enable the recovery of valuable metal powders from various sources, such as electronic, industrial, and automobile scrap. Mechanical alloying is a potential opportunity for sustainable powder production as it has the capability to convert various starting materials with different initial sizes into powder particles through the ball milling process. Nevertheless, parameter factors, such as the type of ball milling, ball-to-powder ratio (BPR), rotation speed, grinding period, size and shape of the milling media, and process control agent (PCA), can influence the quality and characteristics of the metal powders produced. Despite potential drawbacks and environmental impacts, this process can still be a valuable method for recycling metals into powders. Further research is required to optimize the process. Furthermore, ball milling has been widely used in various industries, including recycling and metal mold production, to improve product properties in an environmentally friendly way. This review found that ball milling is the best tool for reducing the particle size of recycled metal chips and creating new metal powders to enhance mechanical properties and novelty for mold additive manufacturing (MAM) applications. Therefore, it is necessary to conduct further research on various parameters associated with ball milling to optimize the process of converting recycled copper chips into powder. This research will assist in attaining the highest level of efficiency and effectiveness in particle size reduction and powder quality. Lastly, this review also presents potential avenues for future research by exploring the application of RT in the ball milling technique.

The present study is focused on polylactic acid (PLA) blending with bio nanoadditives, such as Tonsil^® (clay) and Aerosil^®, to obtain nanocomposites for a new generation of food packaging. The basic composition was enhanced using Sorbitan oleate (E494) and Proviplast as plasticizers, increasing the composite samples’ stability and their mechanical strength. Four mixtures were prepared: S1 with Tonsil^®; S2 with Aerosil^®; S3 with Aerosil^® + Proviplast; and S4 with Sabosorb. They were complexly characterized by FT-IR spectroscopy, differential scanning calorimetry, mechanical tests on different temperatures, and absorption of the saline solution. FTIR shows a proper embedding of the filler component into the polymer matrix and DSC presents a good stability at the living body temperature for all prepared samples. Micro and nanostructural aspects were evidenced by SEM and AFM microscopy, revealing that S3 has the most compact and uniform filler distribution and S4 has the most irregular one. Thus, S3 evidenced the best diametral tensile strength and S4 evidenced the weakest values. All samples present the best bending strength at 18 °C and fair values at 4 °C, with the best values being obtained for the S1 sample and the worst for S4. The lack of mechanical strength of the S4 sample is compensated by its best resistance at liquid penetration, while S1 is more affected by the liquid infiltrations. Finally, results show that PLA composites are suitable for biodegradable and disposable food packages, and the desired properties could be achieved by proper adjustment of the filler proportions.

In recent years, natural materials are becoming a valid alternative to traditional sound absorbers due to reduced production costs and environmental protection. This study explores alternative usage of sheep wool as a construction material with improved sound absorbing properties beyond its traditional application as a sound absorber in textile industry or using of waste wool in the textile industry as a raw material. The aim of this study was to obtain materials with improved sound-absorbing properties using sheep wool as a raw material. Seven materials were obtained by hot pressing (60 ÷ 80 °C and 0.05 ÷ 6 MPa) of wool fibers and one by cold pressing. Results showed that by simply hot pressing the wool, a different product was obtained, which could be processed and easily manipulated. The obtained materials had very good sound absorption properties, with acoustic absorption coefficient values of over 0.7 for the frequency range of 800 ÷ 3150 Hz. The results prove that sheep wool has a comparable sound absorption performance to mineral wool or recycled polyurethane foam.

The aim of this work is to obtain new materials with improved sound absorbing and thermal properties, using rigid or flexible polyurethane foam reinforced with recycled fir sawdust from wood processing as well as by optimizing their mixing ratio. In this respect, we prepared and characterized samples by mixing rigid polyurethane foam (RPUF)/flexible polyurethane foam (FPUF) with 0, 35, 40, 45, and 50 wt% fir sawdust (FS) with grains size larger than 2 mm. The samples were evaluated by cell morphology analysis, sound absorption, and thermal insulation performance. The obtained composite materials containing 50% sawdust have superior acoustic properties compared to those with 100% FPUF in the range of 420–1250 Hz. The addition of 35% and 50% FS in the FPUF matrix led to improved thermal insulation properties and decreased thermal insulation properties in the case of RPUF. The results show that the use of FS-based composites with the FPUF/RPUF matrix for sound absorption and thermal insulation applications is a desirable choice and could be applied as an alternative to conventional synthetic fiber-based materials and as a recycling method of waste wood.

The steel industry is responsible for one-third of all global industrial CO₂ emissions, putting pressure on the industry to shift forward towards more environmentally friendly production methods. The metallurgical industry is under enormous pressure to reduce CO₂ emissions as a result of growing environmental concerns about global warming. The reduction in CO₂ emissions is normally fulfilled by recycling steel waste into alkali-activated cement. Numerous types of steel waste have been produced via three main production routes, including blast furnace, electric arc furnace, and basic oxygen furnace. To date, all of the steel waste has been incorporated into alkali activation system to enhance the properties. This review focuses on the current developments over the last ten years in the steelmaking industry. This work also summarizes the utilization of steel waste for improving cement properties through an alkali activation system. Finally, this work presents some future research opportunities with regard to the potential of steel waste to be utilized as an alkali-activated material.